Can I have onScrollListener for a ScrollView?

Question

Every instance of View calls getViewTreeObserver(). Now when holding an instance of ViewTreeObserver, you can add an OnScrollChangedListener() to it using the method addOnScrollChangedListener().

You can see more information about this class here.

It lets you be aware of every scrolling event - but without the coordinates. You can get them by using getScrollY() or getScrollX() from within the listener though.

scrollView.getViewTreeObserver().addOnScrollChangedListener(new OnScrollChangedListener() {
    @Override
    public void onScrollChanged() {
        int scrollY = rootScrollView.getScrollY(); // For ScrollView
        int scrollX = rootScrollView.getScrollX(); // For HorizontalScrollView
        // DO SOMETHING WITH THE SCROLL COORDINATES
    }
});

This might be very useful. Use NestedScrollView instead of ScrollView. Support Library 23.1 introduced an OnScrollChangeListener to NestedScrollView. So you can do something like this.

 myScrollView.setOnScrollChangeListener(new NestedScrollView.OnScrollChangeListener() {
        @Override
        public void onScrollChange(NestedScrollView v, int scrollX, int scrollY, int oldScrollX, int oldScrollY) {
            Log.d("ScrollView","scrollX_"+scrollX+"_scrollY_"+scrollY+"_oldScrollX_"+oldScrollX+"_oldScrollY_"+oldScrollY);
            //Do something
        }
    });

Here's a derived HorizontalScrollView I wrote to handle notifications about scrolling and scroll ending. It properly handles when a user has stopped actively scrolling and when it fully decelerates after a user lets go:

public class ObservableHorizontalScrollView extends HorizontalScrollView {
    public interface OnScrollListener {
        public void onScrollChanged(ObservableHorizontalScrollView scrollView, int x, int y, int oldX, int oldY);
        public void onEndScroll(ObservableHorizontalScrollView scrollView);
    }

    private boolean mIsScrolling;
    private boolean mIsTouching;
    private Runnable mScrollingRunnable;
    private OnScrollListener mOnScrollListener;

    public ObservableHorizontalScrollView(Context context) {
        this(context, null, 0);
    }

    public ObservableHorizontalScrollView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public ObservableHorizontalScrollView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        int action = ev.getAction();

        if (action == MotionEvent.ACTION_MOVE) {
            mIsTouching = true;
            mIsScrolling = true;
        } else if (action == MotionEvent.ACTION_UP || action == MotionEvent.ACTION_CANCEL) {
            if (mIsTouching && !mIsScrolling) {
                if (mOnScrollListener != null) {
                    mOnScrollListener.onEndScroll(this);
                }
            }

            mIsTouching = false;
        }

        return super.onTouchEvent(ev);
    }

    @Override
    protected void onScrollChanged(int x, int y, int oldX, int oldY) {
        super.onScrollChanged(x, y, oldX, oldY);

        if (Math.abs(oldX - x) > 0) {
            if (mScrollingRunnable != null) {
                removeCallbacks(mScrollingRunnable);
            }

            mScrollingRunnable = new Runnable() {
                public void run() {
                    if (mIsScrolling && !mIsTouching) {
                        if (mOnScrollListener != null) {
                            mOnScrollListener.onEndScroll(ObservableHorizontalScrollView.this);
                        }
                    }

                    mIsScrolling = false;
                    mScrollingRunnable = null;
                }
            };

            postDelayed(mScrollingRunnable, 200);
        }

        if (mOnScrollListener != null) {
            mOnScrollListener.onScrollChanged(this, x, y, oldX, oldY);
        }
    }

    public OnScrollListener getOnScrollListener() {
        return mOnScrollListener;
    }

    public void setOnScrollListener(OnScrollListener mOnEndScrollListener) {
        this.mOnScrollListener = mOnEndScrollListener;
    }

}

You can use NestedScrollView instead of ScrollView. However, when using a Kotlin Lambda, it won't know you want NestedScrollView's setOnScrollChangeListener instead of the one at View (which is API level 23). You can fix this by specifying the first parameter as a NestedScrollView.

nestedScrollView.setOnScrollChangeListener { _: NestedScrollView, scrollX: Int, scrollY: Int, _: Int, _: Int ->
    Log.d("ScrollView", "Scrolled to $scrollX, $scrollY")
}